SOILS FERTILIZERS. 519 



period of greatest growth. The water-soluble calcium showed variations 

 similar to those observed in potash. Humus was highest in the most pro- 

 ductive plats. Those plats which showed the lowest percentage of moisture 

 contained the largest amount of nitrogen associated with humus. The total 

 nitrogen varied with the productive capacity of the plats. The condi- 

 tions for nitrate production were most favorable under corn. In com- 

 parative tests of extract soils growing corn, oats, wheat, clover, and timothy, 

 it was found that untreated exti'acts from corn soil gave the best results. The 

 results with the extracts were in general in accord with the productive power 

 of the plats as determined in the field tests. " The plats in other crops did not 

 furnish extracts as favorable to the development of the wheat plant indicator 

 as the tier in corn, nor were the results in accord with field practice. After 

 treating these extracts with purifying substances like carbon black, the actual 

 development was improved and the average results of many experiments then 

 indicate a correlation with field results. 



" It would seem, then, that the gi'owing crop exerts an influence upon the soil 

 solution in situ ; an influence transmitted to the extracts prepared in the labora- 

 tory from fresh soil samples, but removable to a certain extent by treatments 

 with absorbents, such as carbon black or ferric hydrate." 



Contribution to the study of the relations between the fertility of the soil 

 and the phosphoric acid soluble in water, I. Pouget and D. Chough ak (Rev. 

 Gen. Chim., 13 (1910), Nos. 10, pp. 157-178, figs. 9; 11, pp. 198-201; abs. in 

 Chem. Ztg., 3^ (1910), No. 78, Repcrt., p. 3/3).— The relation of water-soluble 

 phosphoric acid, determined by the authors' colorimetic method (E. S. R., 21, 

 p. 105), to productiveness as determined in pot experiments with wheat was 

 studied with 17 soils. 



It was found, as Schloesing has shown, that the rate of solution of the phos- 

 phoric acid of the soil in water decreases more or less rapidly with successive 

 extraction until it becomes practically constant. The authors therefore con- 

 clude that the phosphoric acid is present in two different forms, the first 

 probably phospho-huniates, very soluble in water, the second, probably the min- 

 eral phosphates, much less soluble. The first has a marked effect in the early 

 stages of growth, but in poor soils the rate of solubility of the second determines 

 the final yield, since, according to the authors, the yield is dependent upon the 

 concentration of phosphoric acid in the soil solution. This they maintain is by 

 no means constant for all soils. 



The absorption of phosphoric acid in soils by plants, I. Pouget and I). 

 Chouchak (Rev. Gen. Chim., 13 (1910), No. 12, pp. 219-222; abs. in Chem. Ztg., 

 S.'t (1910), No. 78, Repert., p. 3i3).— This is an account of the investigations 

 noted above. 



The conservation of the fertility of the soil, A. D. Hall (Jour. Bd. Agi. 

 [London^, 17 (1910), No. 2, pp. 11 J,- 123). —This paper deals especially with 

 changes in the nitrogen content of soils, "because though phosphoric acid, 

 potash, and lime are important factors in plant nutrition, those elements are not 

 susceptible to the gains and losses from external operations like cultivation, by 

 which the stock of nitrogen is so greatly affected." The factors which give rise 

 to gain or loss of nitrogen in the soil are discussed on the basis of observations 

 on various plats at the Kothamsted Station. 



The general conclusion reached is " that with every system of farming a cer- 

 tain position of equilibrium will be reached (viewed over a term of years long 

 enough to smooth out seasonal effects) when the natural recuperative agencies 

 and the additions of fertilizing material in the manure are i)alance<l l>y the 

 removals in crops and stock and the inevitable waste. The higher the Ifvel of 

 production, the greater will be the waste, and, iu cousequeuce, the additions of 



